In today's motor vehicles, the driving internal combustion engine is usually provided with a starter motor, and in addition, it drives a generator via a belt pulley. In future vehicle concepts, increasingly powerful electrical machines are installed which replace both the present generator and the conventional starter motor. Besides the internal combustion engine, if these electrical machines also contribute to driving the motor vehicle, as a rule, one speaks of hybrid vehicles. Among hybrid vehicles, parallel hybrids are known, for example, in which, in addition to the internal combustion engine, one or more electrical machines are integrated into the power train. Power-splitting hybrid concepts are also known, in which two electrical machines are mounted in such a way that the mechanical power originating from the internal combustion engine contributes both directly and indirectly to the driving power at the wheels, via the two electrical machines.
Such electrical machines could, in principle, be operated in different types of operation and operating conditions, such as in a dynamically optimal operating state or in an optimal efficiency operating state. The dynamically optimal operating state stands out in that an engine torque build-up can take place very rapidly in response to a corresponding requirement, for instance, having a time factor of 5–10 ms. What is disadvantageous about the dynamically optimal operating state is the poor efficiency, since thereby the flux-forming current component is generally held at its nominal value, that is, independent of a torque requirement. In the optimal efficiency operating state there is a favorable efficiency, but on the other hand one may expect a torque-setting time that is longer by a factor of 10.